Find min/max value from a __m128i

Question

I want to find the minimum/maximum value into an array of byte using SIMD operations. So far I was able to go through the array and store the minimum/maximum value into a __m128

Answer 1

Here is an example for horizontal max for uint8_t:

#include "tmmintrin.h" // requires SSSE3

__m128i _mm_hmax_epu8(const __m128i v)
{
    __m128i vmax = v;

    vmax = _mm_max_epu8(vmax, _mm_alignr_epi8(vmax, vmax, 1));
    vmax = _mm_max_epu8(vmax, _mm_alignr_epi8(vmax, vmax, 2));
    vmax = _mm_max_epu8(vmax, _mm_alignr_epi8(vmax, vmax, 4));
    vmax = _mm_max_epu8(vmax, _mm_alignr_epi8(vmax, vmax, 8));

    return vmax;
}

The max value will be returned in all elements. If you need the value as a scalar then use _mm_extract_epi8.

It should be fairly obvious how to adapt this for min, and for signed min/max.